1. Field of the Invention
The present invention relates to a slot array antenna using a slot antenna portion which has a linear strip-shaped power supply line formed on one surface of a dielectric substrate and a plurality of slots formed in a conductive layer on the other surface of the dielectric substrate.
2. Description of the Related Art
In the past, such types of slot array antennae with directionality have widely been used for receiving radio waves coming from a desired direction, or for transmitting radio waves in a desired direction. Among these slot array antennae, a planar antenna constructed on a dielectric substrate is advantageous for reduction in size and weight thereof.
With such a slot array antenna having a plurality of slots formed on a dielectric substrate, there are the following two cases. That is, one case is that only a single element or slot is supplied with power, and the other case is that a plurality of elements or slots are supplied with power. In the former case, those elements other than the one supplied with power are made to function as reflectors or director. In contrast, in the latter case, a plurality of elements or slots are oscillated to provide a desired characteristic by adjusting the amplitude and phase given to each element in an appropriate manner. In this case, a micro-strip line is utilized as the power supply line for concurrently supplying power to the plurality of elements. In addition, there is another type of slot array antenna with slots directly formed in a power supply line in the form of wave guides without using a dielectric substrate.
With the conventional slot array antennae as referred to above, particularly in the case of using wave guides, it is difficult to machine and assembly them with high precision, and in the case of a slot array antenna having slots formed on a dielectric substrate, inter-slots coupling can not be neglected and hence it is also difficult to perform desired circuit designing while taking such inter-slots coupling into consideration.
The present invention is intended to obviate the above-mentioned problems encountered with the conventional slot array antennae, and has for its object to provide a novel and improved slot array antenna with a cavity which has slots formed on a dielectric substrate but is capable of providing good transmission directional characteristics while minimizing or disregarding inter-slots coupling.
Bearing the above object in mind, according to one aspect of the present invention, there is provided a slot array antenna with a cavity comprising: a slot antenna portion having a plurality of slots arranged in an arrayed fashion; and a reflector with a cavity having an opening disposed in opposition to a plane on which the plurality of slots exist.
Preferably, the cavity serves to cut off a frequency xcex of radio waves to be used. Specifically, assuming that the width and depth of the cavity are xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d, respectively, for the frequency xcex to be used, then the relationship between the width xe2x80x9caxe2x80x9d and the length xe2x80x9cbxe2x80x9d of the cavity is as follows:
a less than b and a less than (xcex/2)
Preferably, the slot antenna portion comprises: a dielectric substrate having a first surface and a second surface; a power supply line disposed on the first surface of the dielectric substrate; and a conductive layer disposed on the second surface of the dielectric substrate.
Preferably, the cavity has a width less than xcex/2.
Preferably, the slot antenna portion comprises: a dielectric substrate having a first surface and a second surface; a power supply line disposed on the first surface of the substrate in close contact therewith so as to extend in a rectilinear strip-shaped fashion; and a conductive layer formed on the second surface of the dielectric substrate and having the plurality of slots formed therein in such a manner as to extend perpendicularly to the power supply line with the dielectric substrate interposed therebetween.
Preferably, the power supply line comprises a micro-strip line.
According to another aspect of the present invention, there is provided a slot array antenna system with cavities of a sector antenna type comprising: a plurality of sectors; and a plurality of slot array antennae each referred to above, the slot array antennae being disposed one for each of the plurality of sectors.
In a preferred embodiment of the invention, the slot array antenna with a cavity has a slot antenna portion 10 with a plurality of slots 14a, 14b, 14c, 14d arranged in an array, and a reflector 40 with a cavity 42 having an opening disposed in opposition to a plane on which the plurality of slots 14a, 14b, 14c, 14d exist.
With such an arrangement, the cavity of the reflector serves to diminish inter-slots coupling (i.e., coupling between the slots) to thereby adjust the directionality created by the slot antenna portion, so that a beam transmitted from or received by the slot antenna portion can be oriented in a desired direction, thus improving the directionality and the F/B ratio (i.e., front to back ratio) thereof. In this case, when the cavity functions to cut off the frequency of radio waves to be used, these characteristics can further be improved.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of presently preferred embodiments of the invention taken in conjunction with the accompanying drawings.